Tuesday, September 18, 2007

Urban Forests and Clean Air

Part 4 of the six part series on Pune city pollution and environment. Updated every Tuesday.

Tropical forests are extremely important to the global carbon cycle. These forests remove a high proportion of carbon dioxide being emitted by industries and through deforestation. Human activities emit around 25 billion tons of carbon dioxide (CO2) every year. Out of that about 30% is absorbed by the oceans, about 40% stays in the atmosphere and about 30% is thought to be absorbed by forests. Temperate forests are less efficient in sucking in CO2 as compared with tropical forests. But the amount of forest cover is steadily decreasing thus increasing the amount of CO2 that stays in the atmosphere. Deforestation is the second biggest emitter of CO2 after power generation as can be seen in the figure below on greenhouse gas emissions by source (source: World Resources Institute).

In general mature forests are not net absorbers of CO2, since they give up almost as much CO2 through rotting biomass. New growth forests are more efficient absorbers of CO2. So planting trees and expanding forest cover rather than just maintaining forests will lead to offsetting of CO2 emissions.

Right on! Trees as life givers of oxygen (I often wonder why people don't choke to death in deserts), trees as the lungs of our city, save trees and breathe better, all these have become popular slogans. Here are a few more from Pune environmentalists:

"..these green areas give Oxygen....(for us humans..and this is the only source of Oxygen on the planet), help to reduce pollution, and preserve our eco-environment" in this article

and recently (Times of India, Sept 13 07, Pune) by noted environmentalist Anita GokhaleBenninger" An average Pune family size of five people will require 60 sq metres of green areas to breathe and survive. Once preserved and re-forested, the PuneBDP (biodiversity parks) will provide clean air for approximately 35 lakh (3.5 million) people living in this area"

The ability of trees to absorb CO2 has lead to an unquestioned faith in their ability to provide us with clean air. But can trees provide us with that service?

Let's take pollutants that harm us now, and pollutants that will harm us in the future.

Vehicles in Pune emit several hundred to thousands of tons of harmful pollutants like SOx, NOx, HC and PM10 (particulate matter) every year. These are having immediate health effects on citizens. But trees do not absorb these chemicals. No amount of tree plantations will have any effect on the amounts of these pollutants in the air. Ultimately only better quality fuel and to a certain extent a better public transport system will have any appreciable impact on Pune air quality. But trees also absorb dust. Won't that reduce for example the amounts of particulate matter. Ms. Benninger recently calculated that trees in the proposed biodiversity parks will trap around 80 thousand tons of dust per year. The problem is that a large proportion of particulate matter that harms citizens is adsorbed on dust lying of unclean and unpaved roads. Pune Municipal Corporation Env. Status report 2006-07 indicates that nearly 6 thousand tons of particulate matter adsorbed on dusty roads get suspended by vehicular traffic. This is the dust that harms citizens health. The solution for this problem is not trees on hills but better paved roads which are cleaned regularly.

And what about pollutants like CO2, which through its effect on global warming will harm us in the near future? Is the tree cover in Pune offsetting sufficient amounts of CO2 emitted from vehicles? The discrepancy is startling. Here are two examples:

The forest cover on Law College Hill and VetalTekdi absorbs about 1.5 tons of CO2 per year. In contrast, idling your vehicle for 5 minutes at Nal Stop every day, will lead to emission of about 625 tons of CO2 per year (amount calculated for total number of vehicles passing through Nal Stop every year).

The total amount of CO2 absorbed by the tree cover in Pune is about 55 thousand tons per year. In contrast, vehicles emit about 2 million tons of CO2 per year.

So Pune tree cover cannot save us from the increasing amount of CO2 emissions either. Increased plantations especially on the hills will help increase the amounts of CO2 absorbed, but I feel they will play no significant role in offsetting vehicular emissions.

Image below shows managed forest on Pune hills.

The second topic I want to briefly touch on is the reporting on the proposed biodiversity parks on the hills. There are complex legal issues involved in this since the ownership of the hills is split between the forest department, the government and private land owners. A significant portions of the hills have been encroached upon by slums. Recently from an environmental perspective the reporting has focused upon carbon trading schemes and whether they can generate funds for land acquisition. The basic idea is to use plantations on Pune hills to offset CO2 emissions and get paid for every ton of CO2 absorbed. Supporters of this scheme say that significant amounts of funds can be generated by plantations on Pune hills. Here is a summary of a recent calculation by Ms. Benninger (Times of India, Sept 13, 07, Pune):

The amount of hill land is 1646.74 hectares. Each forest hectare will absorb around 55 tons of carbon per year. Therefore the total amount of carbon absorbed per year will be 90,530 tons. Carbon credits are presently sold for around $12 per ton of CO2 eq. (my link) and will increase in the near future. So amount of funds generated per year will be around 4.88 crore.

First some technicalities. Some of the hill land is already built upon legally and will in reality never be available for any plantations. Further, is it 55 tons of carbon or carbon dioxide? If it is carbon that means almost 200 tons of CO2 will be absorbed per forest hectare per year (one ton Carbon combines with oxygen to give 3.62 tons CO2). Either way, 55 tons absorption of carbon or carbon dioxide is a gross exaggeration (doesn't the media ever do any background checks?). Amount of CO2 absorbed per forest hectare varies depending on the climate (temperate or tropical) , soil quality, and species of trees. Generally the range is from about 6 tons per year for temperate areas to anywhere from 5 tons to 20 tons per year for tropical areas.

All these amounts are for managed plantations. Currently our forest on various hills (few hundred hectares) are absorbing in totality around 3-4 tons of CO2 per year. This is an abysmally low figure but not very surprising if you are to walk on these hills. The vegetation is stunted and sparse. It sheds leaves starting December and lies bare until the monsoons. By February the forest department starts burning the underbrush as part of their forest management plan. This means emissions of CO2. I doubt if there is any net absorption of CO2 by these forests, especially in the more mature stands. Considering the rocky soils of the hills, no amounts of additional plantations will raise CO2 absorption to a quantity that can generate any significant funds. Besides, environmentalists agree that even the dubious 4.88 crore per year they have calculated is too little an amount for land acquisition, which will require according to estimates several 100 crores.

On this funding issue, the Maharashtra government has been disingenuous. They have transferred the burden of coming up with the funds for the biodiversity parks onto the Pune Municipal Corporation and are refusing to pass the green development plan for the city, which has earmarked the hill areas as biodiversity zones. However, large amounts of money which will unlock land on the hills especially through slum rehabilitation is tied to the Jawaharlal Nehru National Urban Renewal Mission, a central government scheme to modernize Indian cities. The centre will not release that money to the Maharashtra government until they repel the Urban Land Ceiling Act , which the Maharashtra government is hesitating to do. That really should be the thrust of the arguments made by the PMC and environmentalists in the effort to acquire land for the biodiversity parks.

In summary, regarding the biodiversity parks, I feel carbon trading schemes will not generate any appreciable funds. Besides, the very nature of carbon trading schemes through plantations is incompatible with what should be the real goal of the biodiversity parks, which is maintaining and expanding biodiversity. Trading schemes require that plantations consist of rapidly growing trees. Even though indigenous species will be preferred, it would inevitably mean that the plantations will consist of only one or two rapidly growing indigenous tree species, defeating the purpose of developing and maintaining biodiversity.

Trees on Pune hills will not provide citizens with clean air nor will they significantly offset CO2 emissions. The real value of urban forests on these hills is that they provide citizens with open recreational areas, and if properly developed will create expanded habitats for land animal and bird species, thus genuinely contributing to rich urban biodiversity. That by itself is a goal worth fighting for.

1 comment:

I do think planting of trees on the hill is a good idea. but the trees should be of species which would grow in the rocky soil of the hills. You have not though touched on the subject of unused land which could be acquired by the PMC in every area which is coming up, and use that for bio diversity parks, which would also be centres for the public to enjoy clean air!

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ABOUT THIS BLOG

I am a Sedimentary Geologist. On Rapid Uplift I write mostly about topics within the geosciences, but sometimes on biological evolution and environmental issues. I like to travel and in my free time I teach 12 year old kids soccer and rugby.